Google seems to disappoint when it comes to quite vague combinations of terms like these—at least if you don’t already have a degree in electronics! So I would greatly appreciate advice from our electronics-/engineering-savvy members. I think this thread is roughly on-topic.

I just bought an old synth. I quickly became disappointed and, just as much, baffled when I realised that any time it’s playing more than one note, it generates horrendous clipping in any speakers or soundcards to which it is connected. The signal appears to be clipping, but it unfortunately doesn’t seem quite that simple, because…

I then discovered this problem does not occur on headphones, which reproduce the synth just fine, as I expected it to sound on the other devices. Also, it sounds pretty quiet there, and indeed, this synth has been claimed to have a low output before. So, the clipping isn’t intrinsic to the outputs, but they’re definitely doing something that speakers, etc. don’t like, causing said devices to read a signal that clips hugely. Because of the low output on headphones, I can’t see how the problem could be due to the outputs being simply too loud/hot, and so I think some other electronic factor must be at work.

What in the world is going on here? Is there any way to assess, and preferably to fix, it? Bear in mind that my knowledge of electronics is, to be charitable, extremely slight. A friend and I think it’s most likely an issue with impedance, perhaps due to the higher-impedance(?) speakers and soundcards drawing a more powerful signal than they should due to some load(?) introduced earlier in the circuitry. However, we can’t make a single guess beyond that and can’t see any component in the pre-amp that is different from what the schematic says it should be. I seem to recall hearing that it may as well be impossible to calculate the impedance introduced by the entire circuit, including the majority that lies beyond the preamps.

Another confusing aspect of this is that the clipping seems to occur only when I try to play more than one voice (read: note) at a time. This makes me wonder if the pre-amp was somehow ‘normalised’ to the maximal no-clip gain for a single voice without any regard for what would happen when something as basic as polyphony was thrown into the mix.

I don’t suppose it’s as simple as shoving a large resistor into the circuit somewhere. :/ Any advice that might help me to salvage this unit will be hugely appreciated. I hope someone might recognise this symptom and be able to suggest the most likely cause—and, with any luck, a feasible solution. Thanks!

Edit: To be clear, this isn’t an intrinsic incompatibility of this type of synth with speakers or soundcards, for I have another one that works just fine. And, again, we couldn’t find any differences between the two that could logically have any affect upon the preamp whatsoever.

Edit again: It has stereo outputs, which naturally have seemingly identical preamps, and both exhibit this problem.